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61.
This study deals with solar hydrogen production from the two-step iron oxide thermochemical cycle (Fe3O4/FeO). This cycle involves the endothermic solar-driven reduction of the metal oxide (magnetite) at high temperature followed by the exothermic steam hydrolysis of the reduced metal oxide (wustite) for hydrogen generation. Thermodynamic and experimental investigations have been performed to quantify the performances of this cycle for hydrogen production. High-temperature decomposition reaction (metal oxide reduction) was performed in a solar reactor set at the focus of a laboratory-scale solar furnace. The operating conditions for obtaining the complete reduction of magnetite into wustite were defined. An inert atmosphere is required to prevent re-oxidation of Fe(II) oxide during quenching. The water-splitting reaction with iron(II) oxide producing hydrogen was studied to determine the chemical kinetics, and the influence of temperature and particles size on the chemical conversion. A conversion of 83% was obtained for the hydrolysis reaction of non-stoichiometric solar wustite Fe(1−y)O at 575 °C. 相似文献
62.
A decision-oriented model to evaluate the effect of land use and agricultural management on herbicide contamination in stream water 总被引:1,自引:0,他引:1
Chantal Gascuel-Odoux Pierre Aurousseau Marie-Odile Cordier Patrick Durand Frederick Garcia Vronique Masson Jordy Salmon-Monviola Florent Tortrat Ronan Trepos 《Environmental Modelling & Software》2009,24(12):1433-1446
Modelling stream water pollution by herbicides in agricultural areas is a critical issue since numerous and incompletely known processes are involved. A decision-oriented model, SACADEAU-Transf, which represents water and pesticide transfer in medium-sized catchments (10–50 km2) is presented. This model aims at evaluating the effect of land use, agricultural practice and landscape on the contamination of stream water in rural catchments. The processes are represented in an easily understandable way with a moderate amount of information, producing semi-quantitative and spatialized outputs. Modelling focuses on the first few months after herbicide application when high levels of contamination are generally observed, by considering transfer through the catchment area via surface and subsurface flow. The surface flow, based on a tree plot network representation of the catchment, is controlled by soil-surface properties and saturated conditions. The subsurface flow based on Topmodel concepts is controlled by the topography. Herbicide transfer is coupled to water transfer by taking into account the main characteristics of the chemicals. The model simulates the daily water and herbicide outflow at the outlets of the farmers' fields as well as from the catchment. Preliminary results on maize herbicide transfer are presented for an agricultural catchment with an area of 17 km2 located in north-western France. The relevance of SACADEAU-Transf model is discussed in view of the qualities required for the decision-oriented models developed for improving agro-environmental management. 相似文献
63.
Florent Monestier Jean-Jacques Simon Philippe Torchio Ludovic Escoubas Franois Flory Sandrine Bailly Remi de Bettignies Stephane Guillerez Christophe Defranoux 《Solar Energy Materials & Solar Cells》2007,91(5):405-410
We have investigated the short-circuit current density of organic solar cells based on poly (3-hexylthiophene)(P3HT)/6,6-phenyl C61-butyric acid methyl ester (PCBM) blend. In order to model charge collection efficiencies with respect to short circuit density in such blends, a full optical modeling of the cell is performed. From the distribution of the electromagnetic field, we compute the rate of exciton generation. This exciton generation rate is used as input in the transport equations of holes and electrons. Charge densities at steady state are obtained as solutions are used for computing short-circuit current densities generated in the cell. The dependence of short-circuit current densities versus the thickness of the blend is analyzed and compared with our experimental data and with data extracted from the literature. 相似文献
64.
Amarilli Antoine Capelli Florent Monet Mikal Senellart Pierre 《Theory of Computing Systems》2020,64(5):861-914
Theory of Computing Systems - The field of knowledge compilation establishes the tractability of many tasks by studying how to compile them to Boolean circuit classes obeying some requirements such... 相似文献
65.
66.
Sophie Didierjean Alain Chenu Thierry Geneston André Rakotondrainibe Gaël Maranzana Erik Rozier Florent Beille Olivier Lottin 《International Journal of Hydrogen Energy》2012
The transient response of proton exchange membrane fuel cells during start-up is an important issue for backup power systems which require a very short start-up time in order to limit the use of batteries during a blackout. The start-up procedure of a ten cells stack was studied: in the first stage the cathode channel initially filled with nitrogen was supplied with oxygen in open circuit then in the second stage it was connected to the load. The influences of the current time-profile (step or ramp), the cell voltage at the connection and the gas flow rates on the voltage variation were investigated. It was found that the voltage value during the filling of the cathode is not sufficient to determine which fraction of the cathode was filled with oxygen. In most cases, high oxygen flow rates allow reducing the start-up time of the stack. Furthermore, for fixed current density and stoichiometric coefficients it was found that a minimum start-up time exits. The analysis of transient response to current steps showed that around 70% of the maximum electrical power was available less than 2 s after the beginning of the start-up procedure. 相似文献
67.
Florent Fournier Dit Chabert Franck Tancret Frédéric Christien René Le Gall Jean-François Castagné 《Journal of Materials Science》2007,42(23):9765-9774
The finite element software Comsol is used to simulate surface or grain boundary segregation in dilute alloys. The model computes
simultaneously the evolution of interfacial concentration and diffusion in the bulk. The solute exchange between bulk and
interface is governed by Darken’s equation. The model is able to reproduce thermodynamic and kinetic aspects of the phenomenon,
in particular the saturation segregation level and the short-time segregation kinetics expressed by the McLean approximation.
It is also able to reproduce experimental trends in the case of surface segregation of sulphur in a Ni superalloy. In the
case of the grain boundary segregation of impurities (P or S) in engineering alloys, the present approach provides a practical
tool, as it can be coupled to other finite element simulations (heat transfer and/or mechanics). Thus, it becomes possible
to predict the risk of synergetic segregation and thermomechanical damage during service or processing (forging, welding,...). 相似文献
68.
69.
The behaviour of the immersed boundary method proposed by Goldstein et al. [Goldstein D, Handler R, Sirovich L. Modelling a no-slip boundary condition with an external force field. J Comput Phys 1993;105:354-66] as a second-order damped control system is investigated. The natural frequency and the damping coefficient are introduced as driving parameters of the method. The comparison between the velocity response at forced points in the startup flow over a square cylinder with the theoretical response of a second-order damped oscillator is performed. The role of each parameter appears clearly. At the beginning of the startup flow, the response time depends directly on the natural frequency, and this parameter determines the level of residual velocities achieved in an unsteady flow. The damping coefficient drives the oscillation of the velocity response at the beginning of the startup flow, but has negligible influence during the establishment and in the unsteady flow. At forced points facing no unsteady perturbation from the flow, the zero-velocity set point is reached asymptotically, as usual in second-order damped-systems. Through the simulation of the flow over a blunt flat plat at Re=1000, it is observed that the initial thickness of the mixing layer due to the separation at the edge may vary during the simulation because the sharpness of the edge increases as the residual velocities decrease. This insight gained on the behaviour of the response allows a time-step optimisation, which, completed with comparisons to reference literature results, confirms the feedback forcing method a competitive tool for accessing near-wall unsteady flow over sharp-edged bodies. 相似文献
70.
Florent Sourbier Stéphane Operto Jean Virieux Patrick Amestoy Jean-Yves L’Excellent 《Computers & Geosciences》2009,35(3):487-495
This is the first paper in a two-part series that describes a massively parallel code that performs 2D frequency-domain full-waveform inversion of wide-aperture seismic data for imaging complex structures. Full-waveform inversion methods, namely quantitative seismic imaging methods based on the resolution of the full wave equation, are computationally expensive. Therefore, designing efficient algorithms which take advantage of parallel computing facilities is critical for the appraisal of these approaches when applied to representative case studies and for further improvements. Full-waveform modelling requires the resolution of a large sparse system of linear equations which is performed with the massively parallel direct solver MUMPS for efficient multiple-shot simulations. Efficiency of the multiple-shot solution phase (forward/backward substitutions) is improved by using the BLAS3 library. The inverse problem relies on a classic local optimization approach implemented with a gradient method. The direct solver returns the multiple-shot wavefield solutions distributed over the processors according to a domain decomposition driven by the distribution of the LU factors. The domain decomposition of the wavefield solutions is used to compute in parallel the gradient of the objective function and the diagonal Hessian, this latter providing a suitable scaling of the gradient. The algorithm allows one to test different strategies for multiscale frequency inversion ranging from successive mono-frequency inversion to simultaneous multifrequency inversion. These different inversion strategies will be illustrated in the following companion paper. The parallel efficiency and the scalability of the code will also be quantified. 相似文献